摘要:

To gain increased insight into the mechanism of living polymerization of isobutylene (IB) and specifically into the effect of the structure of the initiator on the rate, we have investigated the polymerization of IB initiated by eight 2,4,4-trimethylpentyl (TMP) esters RCOO-C(CH3)2C(CH3)3where R = -CCl3, -CHCl2, -CH2C6H5, -CH3-CH(CH3)2, -C(CH3)3, -C6H5, and -CH=CHC6H5in conjunction with BCl3coinitiator using CH3Cl diluent at -30°C. The rates decreased along the sequence of these substituents from very high values (with R = -CCl3, -CHCl2) to very low values (R = -C(CH3)3, -C6H5, -CH=CHC6H5). The trend of decreasing rates was interpreted in terms of inductive effects. According to conversion-time curves obtained with the five esters R = -CH2C6H5, -CH(CH3)2, -C(CH3)3-C6H5, and -CH=CHC6H5, propagation is first order in monomer and the apparent rate constants of propagation decrease along the above sequence, suggesting the presence of inductive effects and the absence of resonance effects. With highly electron-donating substituents, i.e., with R = -CH(CH3)2-C(CH3)3, -C6H5, and -CH=CHC6H5, chain transfer to monomer is operational, the rates of which were found to be monomolecular (zero order in monomer). Chain transfer to monomer can be avoided by increasing the polarization of the C-O bond by using slightly electron-donating or strongly withdrawing substituents (R = -CH2C6H3, -CH3or -CHCl2, -CCl3) or by the use of CH2Cl2; both measures also result in enhanced propagation rate constants. Solvent polarity critically affects the stability of the growing chain end. By decreasing the polarity of the solvent, the decomposition temperature of the growing site decreases, leading to termination. Quenching studies have been carried out with model compounds as well as with polymerization systems and both kinds of experiments indicated the exclusion formation of t-chloro endgroups.

ISSN:0022-233X    

DOI:10.1080/00222339009349649

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Copolymers were prepared by condensing 2,4-dihydroxyacetophenone with 1,4-butane diol in the presence of different amounts of polyphosphoric acid catalyst by using equimolar proportions of two reactants. The copolymer samples were characterized by elemental analysis. The number-average molecular weight was determined by nonaqueous conductometric titrations. Viscosity measurements carried out in DMSO at 35°C indicated normal behavior. Chelation ion-exchange properties were also studied by employing the batch equilibration method. The order of metal selectivity is UO22+> Cu2+> Fe3+> Ni2+.

ISSN:0022-233X    

DOI:10.1080/00222339009349650

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Cloud-point curves, critical points, and coexistence curves with feed concentrations close to the critical concentration were measured in three systems involving cyclohexane + different polydisperse polystyrenes. The shape of the coexistence curves is analyzed by using a scaling expression. In two systems the critical exponent β possesses values somewhat larger than in actual binary systems (where β ≈ 1/3), whereas in the third system a somewhat smaller value is found. By using a three-parameter Gibbs free energy relation, cloud-point curves and coexistence curves are calculated from the critical point data and from the slope of the cloud-point curve at this point. To account for polydispersity, the method of continuous thermodynamics is applied. The cloud-point curves are well described, but the prediction of the coexistence curves is bad due to the mean-field character of the Gibbs free energy relation resulting in β = 1/2. Hence, the often used practice of fitting the parameters of a mean-field Gibbs free energy relation to the critical point and to some cloud points and then to calculate the coexistence data is to be considered with great care.

ISSN:0022-233X    

DOI:10.1080/00222339009349651

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The photoreduction behavior of alkyl viologen compounds in a PVA matrix was investigated. The initial photoreduction of alkyl viologens and related polyviologens follows second-order reaction kinetics, and the respective rate constants, which vary only slightly with alkyl chain length, were determined. While the polymer effect was not remarkable in a PVA matrix, the association behavior of radical cations was similar to that found in a 2-propanol aqueous solution.

ISSN:0022-233X    

DOI:10.1080/00222339009349652

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The radical copolymerization of micelle-forming sodium 11-acry-lamidoundecanoate (Na 11-AAU) with acrylamide (AM) has been studied. The copolymer compositions were determined from elemental analyses and13C NMR. The radical reactivity ratios for Na 11-AAU (M1) and AM (M2) were found to ber1= 0.71 andr2= 0.62. The molecular weights of the copolymers as determined by light scattering ranged from 0.88 to 1.62 × 106. The presence of AM up to 50 mol% in the feed did not seem to affect the molecular weights of the copolymers. However, the radius of gyration of the copolymers increased slightly with the increase of AM. The viscosities of the copolymer solutions also increased with AM content, but they were sharply reduced by the effect of NaCl or on aging at room temperature.

ISSN:0022-233X    

DOI:10.1080/00222339009349653

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Polyoxyethylene macromers were synthesized by polymerization of ethylene oxide in dimethylsulfoxide by using potassium napthalide in tetrahydrofuran as initiator, followed by termination with methacroyl chloride. Potassium naphthalide is more active as an initiator than sodium naphthalide. The initiator in this case was confirmed to be of the monoanionic type. The molecular weight of the macromers can be varied from 2 × 103to 1.2 × 104with Mw/Mn= 1.07-1.12. The macromers were characterized by UV, IR, and1H NMR, and copolymerized with butyl acrylate, methyl acrylate, or methyl methacrylate. The grafting efficiency can reach about 90%. The graft copolymers were purified by extractions and characterized by GPC, IR, and a Bruss membrane osmometer. The average grafting number of the copolymers varied from 10 to 15.

ISSN:0022-233X    

DOI:10.1080/00222339009349654

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Two new azo-benzoin initiators were synthesized by the condensation of 4,4′-azo-bis-(4-cyanopentanoic acid chloride) (ACPC) with benzoin (B) and α-methylolbenzoin methyl ether. The initiator structures were confirmed by IR and NMR spectroscopy. The kinetics of the bulk polymerization of styrene initiated by the azo benzoin initiator, obtained from ACPC and B, was investigated and the kinetic parameters evaluated. The initiation of polymerization of styrene by means of azo-benzoin initiators yields polymers with terminal photoactive benzoin groups.

ISSN:0022-233X    

DOI:10.1080/00222339009349655

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Novel polyamides containing 2,3,6,7-dibenzo-1-thia-4,5-diazacy-clohepta-2,4,6-triene-4′,4″-dicarboxy-l, l-dioxide (VII) are reported. The acid VII was prepared in several steps fromp-chlorobenzoic acid and characterized by spectral data and elemental analysis. Prior to polymer synthesis, a model diamide (MDA) was prepared from VII andp-toluidine. The model diamide and several polyamides were obtained in an overall yield of (75-90%) by direct polycondensation of acid VII with certain diamines through a phosphorylation reaction at 100-110°C employing a solvent mixture of NMP-pyridine. The resulting polyamides and MDA were characterized by spectral, analytical, and thermal methods. The solubility, density, viscosity, and morphology (X-ray) were also studied for the polyamides. These polymers were moderately soluble in conventional polymer solvents, and the inherent viscosities were measured in concentrated sulfuric acid. Integral procedural decomposition temperatures (ipdt) were calculated from their primary thermogram in the temperature range 100-650°C in order to have quantitative data regarding their relative thermal stabilities. The polymers exhibit a 10% weight loss at 500°C in static air.

ISSN:0022-233X    

DOI:10.1080/00222339009349656

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The anionic graft polymerization of vinyl monomers onto carbon fiber initiated by metallized carbon fiber was investigated. The metalation of polycondensed aromatic rings of the carbon fiber surface was achieved by the treatment of carbon fiber with n-butyl-lithium (BuLi) inN, N, N′, N′-tetramethylethylenediamine (TMEDA) or hexamethylphosphorous triamide (HMPT) at 0°C. The anionic polymerization of methyl methacrylate (MMA) and styrene (St) was initiated by the metallized carbon fiber, and these polymers were grafted onto the surface. The conversion and the percentage of grafting increased with increasing amount of BuLi used for the metalation of carbon fiber. When 0.20 g carbon fiber was treated with 0.3 mmol BuLi in TMEDA, the percentage of grafting of PMMA and PSt reached a maximum value (PMMA, 34.5%; PSt, 37.1 %). Furthermore, the metalation of aromatic rings of carbon fiber also proceeds by the treatment with BuLi in HMPT. On the contrary, no grafting was observed when carbon fiber was treated with BuLi in tetrahydrofuran (THF) or toluene. This may be due to the fact that metalation of carbon fiber does not proceed in THF or toluene.

ISSN:0022-233X    

DOI:10.1080/00222339009349657

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A free radical technique is described for the synthesis of tri- and multiblock copolymers of styrene and ethylene oxide through polyethylene oxide-based thermal “iniferters.” The mono- or dihydroxy-terminated oligomeric polyethylene oxides were chemically transformed to the secondary amine terminated species. Thiocarba-mylation and oxidation of the amine groups gave rise to macro- or polymeric thiuram disulfides called macro- or polymeric “iniferters,” respectively. Thermal polymerization of styrene in the presence of the macro iniferter led to the formation of their perfect triblock copolymers, with styrene forming the central block. Utilization of the polymeric iniferter, on the other hand, give rise to (A-B)ntype segmented copolymers containing as many as 3 (A-B) sequences. The length of each block could be regulated by the choice of the appropriate iniferter and its relative concentration with respect to the monomer. The iniferters and the block copolymers were characterized.

ISSN:0022-233X    

DOI:10.1080/00222339009349658

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor